In the past, open-type batteries were troublesome to maintain because the battery decomposes water in the electrolyte during use, so it was necessary to regularly check the specific gravity of the electrolyte, battery voltage and other parameters, and add water to replenish the consumed electrolyte.
Later, sealed batteries appeared, mainly valve-regulated lead-acid batteries (VRLA). Since they do not require water addition, VRLA batteries were called maintenance-free batteries from the beginning, and manufacturers promised a service life of 10 to 20 years (at least 8 years). This gave domestic technicians and maintenance personnel a misunderstanding that such batteries are both durable and completely maintenance-free. Many users basically did not perform maintenance or management after installing the batteries. As a result, in the early 1990s, many new problems that had not been encountered before appeared in VRLA batteries used domestically, such as battery case deformation, electrolyte leakage, insufficient capacity, and uneven terminal voltage. These phenomena occurred not only domestically but also abroad, where VRLA batteries were adopted earlier than in China.
In VRLA batteries, due to higher electrolyte specific gravity and larger float charge current, electrode corrosion is more rapid. Electrode corrosion also consumes oxygen, causing the battery to dry out, which is a unique fault of VRLA batteries. These can all lead to electrolyte leakage. Some VRLA battery faults are caused by malfunctioning gas regulating valves. Cooling of VRLA batteries is more important than for open-type batteries; if insufficient, thermal runaway may cause the battery to melt or explode. Corrosion and fracture of internal terminals, inter-cell connectors, and electrode joints are also more common in VRLA batteries than in open-type batteries. These faults all lead to capacity loss. This makes it difficult for users to grasp the durability and failure issues of VRLA batteries.
User units and management units often only pay attention to the maintenance and management of the equipment part of the backup power supply, while neglecting the significant role of the battery pack. They are unaware that the danger of power failure largely lurks in the battery pack. The charging characteristic of the entire battery pack is that if there are one or more aged batteries with increased internal resistance, their capacity will inevitably decrease. When the charger charges the battery pack, the aged battery will be fully charged quickly due to its small capacity. The charger will mistakenly think that the entire battery pack is fully charged and switch to float charging, charging the battery pack with constant voltage and small current. The remaining healthy batteries cannot be fully charged. The battery pack will charge and discharge based on the capacity of the aged battery. Through the vicious cycle of float charge-discharge-equalizing charge-discharge-float charge, the capacity continuously decreases, and the battery backup time shortens.
Conclusion: If not tested regularly to identify and adjust aged batteries, the capacity of the battery pack will decrease, battery life will shorten, and the efficient and safe operation of the system will be affected.
More rapid electrode corrosion: In VRLA batteries, due to higher electrolyte specific gravity and larger float charge current.
Battery drying out: Electrode corrosion also consumes oxygen, causing the battery to dry out.
Battery melting or explosion: Cooling of VRLA batteries is more important than for open-type batteries.
Corrosion and fracture of internal terminals, inter-cell connectors, and electrode joints are also more common in VRLA batteries than in open-type batteries.
All of these can lead to capacity loss.
The traditional method for battery capacity testing is to perform a full discharge test on the entire battery pack, that is, connect the battery pack to a load bank and discharge it until the cutoff voltage (no power) is reached, to verify the battery capacity. However, this method has many hidden dangers and disadvantages:
